Physics Class 12 NCERT Solutions: Chapter 13 Nuclei Part 13 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Fission Process

Q: 30. Calculate and compare the energy released by (A) fusion of of hydrogen deep within Sun and (B) the fission of of in a fission reactor.


(A) Amount of hydrogen,

, i.e.. , of hydrogen contains atoms.

Of contains atoms.

Within the sun, four nuclei combine and form one nucleus. In this process of energy is released.

Hence, the energy released from the fusion of is:

(B) Amount of


of contains

It is known that the amount of energy released in the fission of one atom of is .

Hence, energy released from the fission of 1 kg of is:

Therefore, the energy released in the fusion of of hydrogen is nearly 8 times the energy released in the fission of of uranium.

Q: 31. Suppose India had a target of producing by of electric power, ten percent of which was to be obtained from nuclear power plants. Suppose we are given that, on an average, the efficiency of utilization (i.e.. conversion to electric energy) of thermal energy produced in a reactor was . How much amount of fissionable uranium would our country need per year by ? Take the heat energy per fission of to be about .


Amount of electric power to be generated,

Of this amount has to be obtained from nuclear power plants.

∴ Amount of nuclear power,

Heat energy released per fission of a nucleus,

Efficiency of a reactor

Hence, the amount of energy converted into the electrical energy per fission is calculated as:

Number of atoms required for fission per year:


1 mole, i.e.. , of contains atoms.

∴ Mass of atoms of

∴ Mass of atoms of

Hence, the mass of uranium needed per year is

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